This invention relates generally to apparatus for forming deep containers from a thermoplastic sheet. More particularly, but not by way of limitation, this invention relates to apparatus for forming deep containers from thermoplastic sheets that includes the use of vacuum as well as mechanical force for deforming the sheet into the cavity to form the deep container while maintaining a substantially constant wall thickness.
Somewhat similar apparatus for forming thermoplastic containers is illustrated in U.S. Pat. No. 4,443,401 issued Apr. 17, 1984 to Howard M. Turner and in an application published under the Patent Corporation Treaty on April 28, 1983 as International Publication No. WO 83/01412.
As mentioned, each of the foregoing discloses apparatus for forming containers from thermoplastic material. Each also uses a plunger to aid in deforming the plastic material and utilizes vacuum to assist in the forming operation. It is not known whether or not apparatus has actually been constructed in accordance with either of the foregoing disclosures, but if they were, such apparatus should operate with reasonable success. However, due to the clamping arrangement, the arrangement of the passageways in the mold portions, and the way in which positive pressure and vacuum is utilized, neither of the disclosures nor any combination thereof teaches the invention as set forth in this application.
One of the difficulties encountered in forming deep containers from thermoplastic material has been the difficulty of maintaining the wall thickness of the container substantially constant. When such wall thickness varies, either weak spots are formed in the container or surface marring occurs due to over-stretching portions of the container walls. Various attempts have been made to alleviate this problem, but none to applicant's knowledge has been entirely successful.
Accordingly, it is an object of this invention to provide apparatus that will form deep containers from a thermoplastic sheet while maintaining a substantially uniform wall thickness.